Temperature sensors are commonly used in a variety of applications including thermostats for homes and for industrial use, safety systems, automotive systems, as well as various self-monitoring electronic systems. For example, a temperature sensor may be included on a same die as other electronic circuitry in order to detect increases in ambient temperature. When a high temperature is detected using such a temperature sensor that exceeds a particular limit, the system may take protective action such as shutting down the entire system or portions of the system. Temperature sensors may be further included in integrated circuits, such as a CPU to provide the temperature information for the whole IC for the purpose of thermal management. This information may be used by the integrated circuit to adjust parameters to improve the performance of the circuit over a certain temperature range.
Temperature sensors may be constructed in a variety of ways. For example, a temperature sensor may be constructed using a bi-metallic strip using two metals having different thermal expansion coefficients. The mechanical deflection of such a bi-metallic strip serves as an indication of the temperature of the bi-metallic stip.
Another way to implement a temperature sensor is electronically using solid state circuitry. For example, the junction voltage of a diode, which has an almost linear temperature dependency with negative slope, may be used to provide a measure of temperature.
In another example, a voltage difference between two diodes having two current densities may also be used to measure temperature. A circuit that uses such a voltage difference is commonly referred to as a proportional to absolute temperature (PTAT) generator, and produces an output signal that has linear temperature dependency with positive slope. To provide a digital output which is related to absolute temperature, a reference voltage is compared to an output signal of the PTAT generator. This reference voltage is expected to be temperature independent, and is typically derived from the PTAT generator by combining a junction voltage of diode and a scaled voltage difference between the two diodes. However, since the junction voltage of diode has some nonlinearity with respect to temperature, the resulting reference voltage has a nonlinear temperature dependency that produces a nonlinearity at temperature sensor's digital output.